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A recent piece reported on National Public Radio had this to say about the experience of having an operation: “Surgery can be a necessary misery, endured in hope of health. But what if you took away the misery, and kept the benefits? When hospitals quit subjecting patients to prolonged fasting […] a study1 finds, patients feel less pain and recover faster.”2 As more research focuses on perioperative outcomes, patients will become increasingly informed about perioperative care, partly due to exposure from the popular news media. This piece, reported on national radio, focused on an enhanced recovery after surgery protocol, which was pioneered over a decade ago in Europe. It is a comprehensive approach to perioperative care that includes enteral hydration and carbohydrate loading up until 2 hours before surgery, as well as goal-directed fluid management, early mobilization, early oral intake after surgery, and a multimodal pain regimen. Carbohydrate loading preoperatively, in the form of glucose-containing solutions, has been shown to reduce postoperative loss of muscle mass, decrease anxiety and hunger, and improve nitrogen balance.3 A Cochrane review noted limited data and issues with protocol compliance but found a reduced length of stay and an overall reduction in complications.4 While the full benefit of enhanced recovery after surgery protocols remains unclear, 1 piece of the protocol deserves attention: reduced fasting. Liberalized fluid intake before surgery has multiple clinical benefits and improves patient satisfaction.5 As Ogino et al.6 describe in an article in this issue of Anesthesia & Analgesia, it is possible that this aspect might actually contribute to decreased pain scores as well.

In a small crossover study investigating the role of hydration status and pain, Ogino et al.6 describe the correlation between dehydration and increased pain perception. Five volunteers were asked to fast for 12 hours and then perform a dehydrating exercise protocol. The study somewhat simulated an operating room experience, with a prolonged fast followed by either oral rehydration up until the dehydration exercise (i.e., surgery) or a prolonged fast and no oral hydration prior to the dehydration exercise. Using cold-pressor tests and functional magnetic resonance imaging, they found that cortical pathways associated with pain as well as the reported pain threshold were altered in the dehydrated group. The group that was allowed oral rehydration had a significantly increased pain threshold compared with that of dehydrated group. The authors hypothesize that the increased sensation of thirst in the dehydrated group led to an amplification of the perception of pain. This might be one explanation for decreased pain scores in patients who are hydrated up until their surgery, and in those who resume oral intake earlier postoperatively. However, it might be possible that a better-hydrated state itself leads to less pain, with or without the perception of thirst.

Dehydration has been shown by others to affect executive functioning, but as far as we know, this is one of the first studies to demonstrate the correlation between pain and dehydration.7 Theoretically, these results would support a protocol that instructs patients to drink clear fluids liberally up until 2 hours before their surgery. The decreased pain levels associated with this approach might in turn reduce opiate use, which could reduce side effects, decrease tolerance, and improve patient satisfaction. This would have the added benefit of reducing the use of excessive intraoperative IV fluids, which has previously been associated with increased ileus and prolonged hospital stay.8,9 However, if we recommend clear fluids preoperatively, are they all the same in benefit and safety?

The nil per os (NPO) guidelines laid out by the American Society of Anesthesiologists suggest that patients can drink “clear liquids” up until 2 hours before their surgery and have no increased risk of aspiration.10 Abstaining from clear liquids starting 4 hours before surgery has actually been shown to increase gastric volumes compared with drinking up until 2 hours beforehand. The American Society of Anesthesiologists defines clear liquid as including, but not limited to, carbonated beverages, clear tea, water, black coffee, and fruit juice without pulp. The “but not limited to” phrase causes most institutions to include chicken broth, JELL-O, and clear sports drinks in their definition of clears. It is well known that fried and fatty foods decrease gastric emptying, and thus, they require an increased fasting period but does the composition of the clear liquid, including protein content, osmolality, glucose concentration, or electrolytes affect gastric volume?

To address this, Nakamura et al.11 evaluated the effect of 2 different types of clear liquids on gastric emptying. They randomized 10 healthy volunteers to either a glucose-containing (1.8%), low-osmolality electrolyte drink or a high-osmolality solution enhanced with the amino acid arginine and 18% glucose. After a period of fasting, the subjects drank 500 mL of either beverage and then underwent magnetic resonance imaging scans of their stomach at 30, 60, 90, and 120 minutes. In the group that drank the low-osmolality, low-glucose/electrolyte solution, all but one had a gastric volume of <25 mL after 2 hours. However, in the group that drank the high-osmolality, high-glucose/arginine solution, no one had a gastric volume below 100 mL at 2 hours. We cannot be sure whether this effect was related to the glucose or protein content or the osmolality. However, what is remarkable is the dramatic difference in gastric volumes after ingesting 2 different types of clear liquids. Also, per personal communication with the author, 50% of the volunteers had a gastric volume greater than 25 mL before drinking the solutions after their 6-hour fasts. The low-glucose-containing solution appeared to enhance gastric emptying, greater than fasting alone.

Together, these studies suggest 2 things: perhaps we should redefine clear liquid, excluding protein or excessive glucose-containing fluids, and we should actually encourage our patients to drink a low-glucose and electrolyte-containing solution before surgery (soft drinks contain about 10% glucose.) While this is mentioned in the American Society of Anesthesiologists fasting guidelines, it seems that in actual practice, patients are still often told to be NPO after midnight. As mentioned in the National Public Radio article, patients describe being NPO after midnight, and all the various other deprivations before surgery as a “necessary misery.” Encouraging patients to drink the right type of liquid up to 2 hours before surgery not only reduces this misery but also actually improves medical outcomes.

RECUSE NOTE

Marcel E. Durieux is Section Editor of Anesthetic Pre-Clinical Pharmacology for the Journal. This manuscript was handled by Spencer S. Liu, Section Editor for Pain Medicine for the Journal, and Dr. Durieux was not involved in any way with the editorial process or decision.

10. American Society of Anesthesiologists C. . Practice guidelines for preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration: application to healthy patients undergoing elective procedures: an updated report by the American Society of Anesthesiologists Committee on Standards and Practice Parameters Anesthesiology. 2011;114:495–511

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